The present invention relates to a CVD film forming method of forming a metal thin film such as Ti film or TiN film by CVD on a substrate.
In forming semiconductor devices, it is known to include metal-based thin films such as a metal wiring layer, a buried layer for electrically connecting layers to each other through a contact hole for connecting a wiring layer situated in an upper layer to a device situated in a lower layer, or through a via hole for connecting an upper layer to a lower layer, and a barrier layer having a two-layered structure of Ti (titanium) film and TiN (titanium nitride) film, formed for the prevention of the diffusion, prior to the formation of the buried layer.
Such metal-based thin films are conventionally formed by physical vapor deposition; however it is becoming very difficult to form, especially, a Ti film or TiN film which constitutes a barrier film on the bottom of a hole by PVD due to the recent trends in command. That is, the devices need to be reduced in size, and the degree of integration should be increased. Further, the width of lines and the diameter of opening holes should be further decreased, and the aspect ratio must be increased.
To meet the above recent trends, a Ti film or TiN film which constitutes a barrier layer, is recently formed by chemical vapor deposition (CVD), with which formation of better quality films can be expected. In the case where a Ti film is formed by CVD, TiCl.sub.4 (titanium tetrachloride) gas and H.sub.2 (hydrogen) gas are generally used as reaction gas, whereas in the case where a TiN film is formed, TiCl.sub.4 gas and NH.sub.3 (ammonium) gas or MMH (monomethylhydrazine) are generally used as reaction gas.
In the case where a thin film described as above is formed directly or indirectly on a semiconductor wafer by the CVD, a high stress is caused on the film formed with the conventional recipe, and a crystal defect or warp is created in the semiconductor wafer after the formation of the film, due to the stress. If a wafer is warped, a crack is made in the film, which causes problems, for example, the center portion and peripheral portion having different values in the depth of focus of the exposing device in the photolithography step. When a crack is made in the film, a conduction error or overetching of an underlying layer is likely to occur.